Electrical outlets in the U.S. generally provide 110 volts, 60 hz and 30-50 amps of electricity. Electrical outlets in Europe generally provide 220 volts, 50 hz and 16 amps of electricity. Most foreign countries have 220 volt systems. RVs built in the U.S. are wired for 110-120 volt systems. The large RVs generally require 50 amperes of current (generally referred to as a 50 A RV) and the smaller ones generally require 30 amperes (generally referred to as a 30 A RV). The electrical appliances in 50 A RVs cannot be fully utilized when connected to electrical outlets in Europe without rewiring at considerable expense amounting to several thousands of dollars. While an ordinary transformer can convert 220 volts to 110 volts with sufficient current for use in a 30 A RV, it cannot work satisfactorily for a 50 A RV since more than one appliance is often used at the same time in the 50 A RV and together may require as much as 50 amps of electrical current in addition to 110-120 volts.
50 A U.S. RVs have cords with four pronged plugs that fit matching receptacles provided in most U.S. campgrounds. 30 A U.S. RVs have electrical cords with three pronged plugs that fit matching receptacles in almost all U.S. campgrounds. Many campgrounds have both receptacles but some have only receptacles suitable for connecting three pronged plugs. An adapter can be employed to connect a four pronged plug from an a 50 A RV to a three prong receptacle. This would, of course, limit output to 30 A and the type and number of appliances that can be used at the same time.